电场强度方向与
轴平行的静电场，其电势
随的分布如图所示，一质量为m、带电量为＋q的粒子（不计重力），以初速度
从O点（
）沿经轴正方向进入电场。下列叙述正确的是
A．粒子从O点运动到
点的过程中，在
点速度最大
B．粒子从
点运动到点的过程中，电势能先减小后增大
C．要使粒子能运动到
处，粒子的初速度
至少为
D．若
，则粒子在运动过程中的最大动能为
D
题目分析:粒子从O运动到x1的过程中，电势升高，场强方向沿x轴负方向，粒子所受的电场力方向也沿x轴负方向，粒子做减速运动；粒子从x1运动到x3的过程中，电势不断降低，根据正电荷在电势高处电势越大，可知，粒子的电势能不断减小，动能不断增大，故在x3点速度最大．故A、B错误；根据电场力和运动的对称性可知：粒子如能运动到x1处，就能到达x4处，当粒子恰好运动到x1处时，由动能定理得：
，解得：
，故C错误；粒子运动到x3处电势能最小，动能最大，由动能定理得：
，解得最大动能
，故D正确。
A young man went to visit a wise man living deep in the mountain for the wisdom of life.
“Excuse me! Could you please tell me what the most day in our lives is？Is it the day when we were born or the day we ？Is it the day when we fall in love or the day we succeed？”The young man asked.
“ The most important day in our lives is today. ”The wise man replied calmly.
“Why？”The young man felt more than . “Is it because there is a moving event taking place today？”
“No. Nothing has happened today. ”
“Is it because of my visit？”
“Even if nobody visited me today, today is very important because today is the only wealth we have. No matter how memorable yesterday is, it has gone by like a ship going down into the sea; no matter how bright tomorrow may be, it is yet to come; but no matter how common today is, it is our control (控制). ”
The young man still wanted to ask something, while the wise man him and said, “When we are talking about the meaning of today, we have a lot of it. ”
The young man nodded and then went down the mountain.
Actually, today is the only we have. So, what we should do now is to yesterday and tomorrow and catch fast today!
| 小题1: | A．important B．necessary C．comfortable D．funny |
| 小题2: | A．miss B．die C．grow D．start |
| 小题3: | A．Nothing B．None C．No one D．Neither |
| 小题4: | A．awful B．pleased C．surprised D．excited |
| 小题5: | A．yet B．already C．ever D．still |
| 小题6: | A．for B．under C．on D．with |
| 小题7: | A．stopped B．refused C．encouraged D．ordered |
| 小题8: | A．treasured B．handed C．wasted D．avoided |
| 小题9: | A．excuse B．way C．chance D．plan |
| 小题10: | A．forget B．remember C．call D．treat |
